Basting can help the skin get brown if the pan drippings you baste with contain meat juice in addition to the fat. The proteins in the turkey juice brown on the skin of the bird same as they do in the bottom of the pan (which creates the fond). This also applies to butter or any other basting liquid that contains protein or sugars.

As a countervailing factor, however, every time you open the oven to baste, the heat drops, thereby reducing the browning effect. And the evaporation of the basting liquid has a slight cooling effect on the skin.

I never understood that either. The only time my turkey baster gets used is for sucking the last bit of water out of the pool filter before we close it for the winter.

I think it was Alton Brown who said that basting a turkey is pretty much useless in improving the flavor — skin is waterproof and nothing gets inside.

Also, opening the oven door to baste lets out heat and screws up the roasting time.